1. Field of the Invention
The present invention relates generally to digital computers and, more particularly, to a digital computer adapted for low power operation while playing a CD-ROM.
2. Description of the Prior Art
Portable computers (i.e., notebook, laptop, palmtop and the like) from major original equipment manufacturers such as Toshiba, Compaq, Dell, IBM and others offer CD-ROM drives as either standard or optional devices. Notebook, laptop, palmtop computers are aimed at the mobile computer user who needs or wants to take work home from the office or on a business trip. An added benefit of CD-ROM equipped portable computers is the opportunity to enjoy periods of relaxation and pleasure by playing audio tracks from standard music CDs. In the ensuing discussion, the term notebook computer will be understood to apply also to laptop, palmtop and other portable, battery powered computers.
The Windows operating system""s media player or third party audio application can play back standard audio CDs on a portable computer. However the simple function of playing an integral audio CD-ROM requires that the entire notebook system be powered for the duration of the audio play back. This causes excessive drain on the notebook""s battery power system, unnecessarily consuming battery energy better saved for CPU intensive use such as word processing and spreadsheet analysis.
Conventional laptop and notebook computers typically have several power down modes. They can be powered down such that the CPU is almost completely off, with the state of the CPU saved on a hard drive. A very low power portion of the CPU or an auxiliary circuit (e.g. keyboard controller) is typically used to recognize when a key is pressed. The system then reactivates normal power to allow the CPU to retrieve the stored machine state from the hard drive thereby restoring the computer into an operating mode. Some well known power saving modes are called sleep mode, suspend mode and the like.
Consequently, a modem energy efficient computer will, over time, operate in several different power management regimes. For example, if a portable computer is being used in an office environment where electrical power consumption is an insignificant concern, then the computer user may want the computer to provide the highest performance and availability possible. Conversely, if the computer is being operated on battery power where there is no convenient source of electrical energy, then the computer user may want to choose a power management regime for the computer that will maximize the time the computer operates without recharging its batteries, even though performance and availability may be noticeably reduced.
To facilitate controlling electrical power consumption in personal computers, Intel Corporation, Microsoft Corporation, and Toshiba Corporation have jointly established an Advanced Configuration and Power Interface Specification (xe2x80x9cACPI Specificationxe2x80x9d). The ACPI Specification Revision 1.0 of Dec. 22, 1996, Copyright 1996 Intel Corporation, Microsoft Corporation, Toshiba Corporation, establishes both a set of five (5) Global System States G3-Mechanical Off, G2/S5xe2x80x94Soft Off, G1xe2x80x94Sleeping, G0xe2x80x94Working, S4xe2x80x94Non-Volatile Sleep, and a set of four (4) Device Power States D0xe2x80x94Fully On, through D3xe2x80x94Off. The ACPI Specification defines the Global System States as follows.
G3 Electrical power is mechanically turned off.
G2/S5 Electrical power is turned on but the computer consumes a minimal amount of power by not executing either user or system computer programs, and the system""s context is not preserved by hardware.
G1 Electrical power is turned on, the system""s context is preserved by hardware or system software, but user computer programs are not being executed.
G0 Electrical power is turned on and user computer programs are executed. In the G0 state, devices such as hard disk drives, CD-ROM drives, floppy diskette drives, etc are dynamically turned on and off as needed.
S4 Electrical power may either be turned off, i.e. Global State G3, or turned on with the computer consuming a minimal amount of power, i.e. Global State G2/S5, while system context is preserved in a non-volatile storage file before entering either the G3 or G2/S5 state, thereby permitting the computer to be restored to its prior operating state, i.e. G1 or G0.
The ACPI Specification further defines Device Power States as follows.
D0 The device is completely active and responsive, and consumes the most electrical power.
D1 A lower power state that is defined for different types of devices which preserves more device context than the yet lower power state D2.
D2 An even lower power state than D1 that is again defined f or different types of devices, and which preserves less device context than state D1.
D3 Electrical power is fully removed from the device, device context is lost, and system software must reinitialize the device when it is turned on again.
The different computer operating modes and associated power management regimes described above are each characterized by a unique power demand (i.e., current drain) from the battery power supply. This is an important feature both in design of portable computer systems, and in marketing them as well. Great attention is focused on minimizing the power demand for each of the different Global and Device operating modes. Thus, the power demand characterizing each power management regime is a critical factor to be considered for portable computers, particularly one that includes a CD-ROM drive for playing audio CDs.
In implementing conventional computer power management strategies, a power management routine (xe2x80x9cPMRxe2x80x9d) executed by the CPU must periodically monitor peripheral devices to assess whether a peripheral device""s operation may be suspended. Similarly, if it becomes necessary to access a peripheral device whose operation has been suspended such as in Device Power modes D1-D3, the PMR must resume that peripheral device""s operation. Generally, suspending the operation of a peripheral device and resuming its operation respectively require that the PMR executed by the CPU perform a unique sequence of operations in turning off electrical power to a peripheral device, and in turning electrical power back on. Writing a computer program that detects a need to execute a power-on or a power-off sequence of operations for a peripheral device is a cumbersome task.
Previous portable computers that include a CD-ROM use PMR functions to minimize battery drain. However, if CPU operation has been suspended to save electrical power, the computer can essentially do nothing. Therefore, in the minimal power drain mode, the CPU cannot use the windows operating system""s media player or third party audio application to play audio CDs.
A significant power drain in portable computers occurs in the conventional LCD monitor. Typically, 60 to 70% of the power consumed by a notebook is consumed by the display. Thus even if a computer""s devices, including even perhaps the CPU, were in a lower power state, i.e., one of the lower Device Power States D1-D3 for power savings during CD-ROM play only, the need to use the normal LCD to display CD-ROM status and the music playing status would itself impede significantly reducing power consumption.
For the reasons described above, it is apparent that a disadvantage of present portable computers for playing audio CDs is that some portion of the computer system must remain energized state to detect key actuation and then to restore power or activate a power restore function of the CPU and associated peripherals (e.g. hard drive, keyboard controller, display, etc.). At times when a portable computer is being used during travel, or when line power is otherwise unavailable, the user may wish to play some audio CDs. Given the limited battery life of most portables, e.g., 3 to 5 hours of use, the user may have to choose to forego using the CD-ROM capability for very long, out of fear that the notebook will not be functional for needed work or communication.
The present invention extends the playing time for a CD-ROM equipped notebook computer while minimizing the loss of potential operating time as a computer.
Another advantage is to select and control the music being played without engaging (powering on) the CPU or other notebook peripherals, i.e., hard drive, display, memory and the like.
Another advantage is to extend playing time and lower power drain while minimizing the requirements for additional software drivers.
Another advantage would be to provide CD-ROM/music status to the user without using the normal display screen with its typically high battery drain requirements.
Another advantage of the present invention is that it facilitates portable computer product differentiation by providing various different audio CD playing user interfaces.
Another advantage of the present invention is that it permits designers of portable computer systems to choose among various different audio CD playing user interfaces.
Another advantage of the present invention is that all of the preceding advantages may be obtained merely by inserting an IC in accordance with the present invention into an existing portable computer design.
In one embodiment the present invention is a digital computer that includes both a computer subsystem and a CD-ROM subsystem. The computer subsystem is conventional and includes a digital computer bus via which various digital computer devices included in the computer subsystem exchange commands and data. Devices included in the computer subsystem include a central processing unit (xe2x80x9cCPUxe2x80x9d), a random access memory (xe2x80x9cRAMxe2x80x9d), a display, a read-write mass storage device, a manual input device, and a digital-audio generating integrated circuit (xe2x80x9cICxe2x80x9d).
The CD-ROM subsystem includes a conventional CD-ROM drive and an audio output amplifier that is coupled to the CD-ROM drive for receiving an analog audio signal from the CD-ROM drive. The CD-ROM subsystem also includes several CD-ROM control buttons for controlling operation of the CD-ROM drive during replay of audio compact disks (xe2x80x9cCDsxe2x80x9d). An audio-interface IC, also included in the CD-ROM subsystem, is coupled to the digital computer bus of the computer subsystem, to the CD-ROM drive, and to the CD-ROM control buttons. The audio-interface IC, in a first operating mode in which the computer subsystem is energized and operating, relays commands and data between the digital computer bus of the computer subsystem and the CD-ROM drive. In a second operating mode in which the computer subsystem is not energized and is inoperative, the audio-interface IC autonomously responds to signals received from the CD-ROM control buttons and transmits commands to the CD-ROM drive which cause the CD-ROM drive to play an audio CD present in the CD-ROM drive.
In a particularly preferred embodiment the present invention the audio-interface IC has a third operating mode in addition to the two described above. In this third operating mode the computer subsystem is energized and operating, and the audio-interface IC receives commands from the CD-ROM control buttons and stores such commands for subsequent retrieval by a computer program executed by the CPU included in said computer subsystem. Furthermore, in this third operating mode, as directed by a computer program executed by the CPU, the audio-interface IC either merely relays commands and data between the computer subsystem""s digital computer bus and the CD-ROM drive, or independently responds to CD-ROM button commands by generating CD-ROM commands internally, and independently transmitting such commands to the CD-ROM drive to control playing an audio CD present in the CD-ROM drive.
An advantage of the present invention is that during playing of audio CDs the invention can double the interval during which the digital computer can operate on a particular amount of battery power.